Re: Router congestion (?) caused by b2 upload-file

On 3 Nov 2020, at 22:32, Rich Brown wrote:

>> On Nov 3, 2020, at 3:15 PM, Thomas Rosenstein 
>> <[email protected]> wrote:
>>
>> Hi all,
>>
>> I have multiple routers which connect to multiple upstream providers, 
>> I have noticed a high latency shift in icmp (and generally all 
>> connection) if I run b2 upload-file --threads 40 (and I can reproduce 
>> this)
>>
>> What options do I have to analyze why this happens?
>>
>> General Info:
>>
>> Routers are connected between each other with 10G Mellanox Connect-X 
>> cards via 10G SPF+ DAC cables via a 10G Switch from fs.com
>> Latency generally is around 0.18 ms between all routers (4).
>> Throughput is 9.4 Gbit/s with 0 retransmissions when tested with 
>> iperf3.
>> 2 of the 4 routers are connected upstream with a 1G connection 
>> (separate port, same network card)
>> All routers have the full internet routing tables, i.e. 80k entries 
>> for IPv6 and 830k entries for IPv4
>> Conntrack is disabled (-j NOTRACK)
>> Kernel 5.4.60
>> 2x Xeon X5670 @ 2.93 Ghz
>> 96 GB RAM
>> No Swap
>>
>> During high latency:
>>
>> Latency on routers which have the traffic flow increases to 12 - 20 
>> ms, for all interfaces, moving of the stream (via bgp disable 
>> session) moves also the high latency
>> iperf3 performance plumets to 300 - 400 MBits
>> CPU load (user / system) are around 0.1%
>> Ram Usage is around 3 - 4 GB
>> if_packets count is stable (around 8000 pkt/s more)
>>
>>
>> for b2 upload-file with 10 threads I can achieve 60 MB/s 
>> consistently, with 40 threads the performance drops to 8 MB/s
>>
>> I do not believe that 40 tcp streams should be any problem for a 
>> machine of that size.
>>
>> Thanks for any ideas, help, pointers, things I can verify / check / 
>> provide additional!
>
> These are the classic symptoms of bufferbloat. I note two indicators: 
> latency jumps 50-100x when uploading, and the decrease in bandwidth 
> (likely caused because ack's are slow to return.) I'm not saying it 
> *is* bufferbloat, but it could be useful to rule it out.
>
> I see you have kernel 5.4, so fq_codel and cake qdisc's should be 
> available. I don't understand enough about your configuration, but 
> you'll want to enable one of those qdisc's "in front of" the 
> bottleneck link so the qdisc can control the queueing. Those qdiscs 
> keep stats to see how much data is queued, how often flow control is 
> given, etc.
>
> I would be curious to hear how this works out.
>

I have downgraded one of the routers from 5.4.60 to the stock CentOS 7 
kernel 3.10.0-514.26.2 and now the issue is GONE
This must be connected to something introduced afterwards!

>>
>> Thomas
>
> Rich